Many proteins essential for the establishment and maintenance of cell polarity contain PDZ domains. I have screened the entire C. elegans genome for new PDZ genes that have roles in cell polarity by determining the loss of function phenotype of each of these PDZ genes using RNA-mediated interference (RNAi). From the set of 58 PDZ genes in the genome, I have identified two new PDZ genes, pdz-1 and pdz-2, that function in epithelial cell polarity. While both pdz-t and pdz-2 are involved in cell polarity, characterization of pdz-1 is the focus of this proposal, as I will focus on its characterization first. I will identify pdz-1 mutants to facilitate a more through characterization of the pdz-1 null phenotype. I will focus on the affect of pdz-1 on the development of the embryonic intestine as these cells are not only one of the first epithelial cells to form but are also very large so that polarity phenotypes can be easily scored. To determine the affect of pdz-1 on epithelial cell polarity, I will determine the localization of apical, basolateral, and junctional proteins in the pdz-1 mutants. I will investigate PDZ-1 function by assessing its subcellular localization, functional domains, and genetic interactions. Finally, I will identify other mutants with pdz-1 like phenotypes, which may allow me to place pdz-1 in a genetic pathway. These analyses will provide an entry point to further our understanding of cell polarity.